Since cured rubbers have excellent heat resistance, chemical resistance and flexibility, they are widely used in automobile parts, consumer electric appliance parts, electric wire covering, parts for medical use. However, in order to produce molded articles using cured rubbers, for example, it is general to be processed through several complicated steps: such as (1) a step of mixing an uncured rubber with a crosslinking agent, an acid accepter, a filler, (2) a step of molding by using an extruder or an injection molding machine, and (3) a step of crosslinking by using a press or an oven, so it takes a long time to obtain a molded article. In addition, there have problems such that rubbers do not melt after being crosslinked, and thus the rubbers can not be subject to post-process such as melt-adhesion.
In order to solve the above-described problems, so called dynamic vulcanization technique has been developed such that crosslinking is conducted while a thermoplastic resin such as polypropylene resin, an uncrosslinked crosslinkable rubber and a crosslinking agent are all together melt-kneading in an extruder.
As a dynamically-vulcanized rubber (TPV), for example, one having a structure in which a crosslinked ethylene-propylene-diene rubber (EPDM) is dispersed in a propylene resin (see, e.g., JP-A-6-287368, JP-A-6-256571 and JP-A-11-228750) is widely studied and practically used in a part.
However, since a matrix is a polypropylene resin, it is a fact that the TPV comprising the above polypropylene resin and a crosslinked EPDM does not have heat resistance at a melting point of a polypropylene resin or more, and chemical resistance is also inferior.
For the purpose of developing TPV excellent in heat resistance and chemical resistance, it is known TPV having a structure that a polyester resin or 4-methyl-1-pentene resin is used as a matrix and a cured rubber is dispersed therein (see, e.g., JP-A-10-212392 and JP-A-11-269330). However, compared with TPV comprising a polypropylene resin and crosslinked EPDM, heat resistance and chemical resistance are somewhat improved in these TPV, but they are not sufficient, and the TPV also has a problem that flexibility and mechanical performance are inferior.
Further, there is studied TPV having a structure that a fluororesin is used as a matrix and a crosslinked fluororubber is dispersed therein as a cured rubber (see, e.g., JP-A-61-57641, JP-A-5-140401 and JP-A-6-228397). Although such TPV has excellent heat resistance and chemical resistance due to a matrix of fluororesins, they have poor low-temperature property, poor flexibility and compression permanent deformation resistance, and not enough mold-processability.